Confinement effects of different retrofitting materials on the axial strength of reinforced concrete columns

This paper discusses the results of experimental research aimed to investigate the potentials of different types of innovative jacketing materials used to retrofit reinforced concrete columns. Carbon fiber reinforced polymer (CFRP) wraps and fiber-reinforced mortar (FRM) jackets were used as retrofitting materials. Steel fibers, synthetic fibers, and cellulose fibers were added as reinforcement to mortar that is used as retrofitting jacket for reinforced concrete columns. To evaluate the effectiveness of these retrofitting techniques, column specimens were prepared and tested. The test results of 9 column specimens with synthetic and cellulose fiber-reinforced mortar jackets, 12 columns with steel fiber-reinforced mortar jackets with 3 different volume fractions (1%, 2%, 3%), and 9 columns retrofitted with CFRP wraps were investigated. The column specimens had square sections with 4-10mm diameter steel as main bars. The dimensions were limited to the size that can be accommodated for axial testing up to failure using a Universal Testing Machine. The confinement effect was quantified by obtaining the individual contribution of each material that comprised the reinforced concrete column specimen and subtracting them from the actual load being resisted. This was done by monitoring the strains of the steel and concrete and relating the measured values to the stress-strain relationships of the materials. The percentage of the confinement effect was obtained in order to evaluate the effectiveness of the contribution of the different materials used in retrofitting techniques. The paper presents the results of the experimental program including the corresponding analysis and comparison of the effectiveness of the different retrofitting materials.